Old friends aren't generally suspicious, although I will get the occasional questioning of my motives or memory (and not necessarily just my memory of that time, but a blanket "oh, well, you might not remember ... you used to use a lot of drugs, right?").

At the moment it's mostly therapy that's bugging me. I understand that 1.) She's still just getting to know me and my life story, so some rehashing of everything is inevitable, and 2.) She's a professional, so maybe she does know better than me what I ought to be talking about. But when I've got pressing stuff going on RIGHT NOW and she wants to talk about my experience in 12 step meetings back in the 1990s, I get a little bit steamed.

she wants to talk about my experience in 12 step meetings back in the 1990s

Uh, what? Wow.

Does she think the changes you're going through right now might trigger a relapse? That really doesn't make sense because while these changes seem stressful, I think they're going to be positive experiences for you. Have you asked her why she wants to talk about it?

I say put your foot down a little - not in a harsh way - and tell her what you want to get out of therapy right now.